Congenital ventricular diverticulum in the brainstem. Report of four cases.

This report concerns rare ventricular malformations observed in four fetal brains. Multiple aqueductal diverticula were the only malformation of the central nervous system (CNS) in one case, unilateral diverticula of the 4th ventricle in a holoprosencephaly and a hydrocephaly, and a ventral accessory aqueduct in a fetus with trisomy 18. These findings are the pathologic progression of embryonal ventricular recesses which may be seen in normal brains.